<custom-style>
  <style>
    html {
      --iron-icon-height: 20px;
      --iron-icon-width: 20px;
      --viewer-icon-ink-color: rgb(189, 189, 189);
      --viewer-pdf-toolbar-background-color: rgb(50, 54, 57);
      --viewer-text-input-selection-color: rgba(255, 255, 255, 0.3);
    }
  </style>
</custom-style>
